The present invention is directed to a combustion pressure peak detector for combustion control of an internal combustion engine and more specifically to a pressure peak detector which can determine the crank angle at the instant when the pressure in the engine cylinder is at a maximum and adjust the ignition timing and air-to-fuel ratio according to the detection signal thereby providing a negative feedback closed loop control of the crank angle when the pressure is maximum.
A similar control device of this type is disclosed by Japanese Patent Application No. 41648/1978. According to this conventional control device, the pressure in the combustion chamber is detected, the crank angle at the instant the pressure is at a maximum is determined from the detection signal and the ignition timing is adjusted at all times so that the difference between the crank angle at maximum pressure and a target value is 0 thereby providing a closed loop control for the crank angle. In order to detect the pressure within the engine cylinder a pickup is provided comprising a ceramic piezo-electric unit which is juxtaposed with the ignition plug in such a manner that the end portion of the pickup is located in the engine combustion chamber. Such an arrangement is disadvantageous in that the construction is intricate, provision for additional space is required for installing the control device on the engine and it is difficult to obtain a large output signal from such a control device. Furthermore, it is necessary to provide special cooling means in order to obtain a stable output from the ceramic piezo-electric unit of the pickup.